National Hellenic Research Foundation, Institute of Biology, Medicinal Chemistry and Biotechnology, 48, Vas. Constantinou Ave., Athens 11635, Greece.
Ultrason Sonochem. 2014 Jan;21(1):35-9. doi: 10.1016/j.ultsonch.2013.05.012. Epub 2013 May 28.
Herein is reported a one-pot three-step process for the regioselective synthesis of 3,5-disubstituted isoxazoles based on copper(I)-catalyzed cycloaddition reaction between in situ generated nitrile oxides (from the corresponding aldehydes) and alkynes, using ultrasound irradiation, avoiding toxic reagents and solvents and isolation/purification of intermediates. The combined use of 40 kHz ultrasonic bath and 20 kHz probe in the presence of copper turnings reduced reaction time to 1h and resulted in only one final purification step with increased yields, clearly indicating that there is a dual-frequency synergistic effect. In addition, under metal free conditions, the 1,3-dipolar cycloaddition was regioselective giving low to modest yields.
本文报道了一种基于铜（I）催化原位生成的腈氧化物（来自相应的醛）与炔烃的环加成反应的一锅三步法区域选择性合成 3,5-二取代异恶唑的方法，该方法使用超声辐射，避免了有毒试剂和溶剂，以及中间体的分离/纯化。在铜丝的存在下，使用 40 kHz 超声浴和 20 kHz 探头的组合将反应时间缩短至 1 小时，仅需进行最后一步纯化即可获得更高的收率，这清楚地表明存在双频协同效应。此外，在无金属条件下，1,3-偶极环加成反应具有区域选择性，得到的产物产率较低至中等。
